Vials are small sealable vessels commonly used as containers for liquids, for example liquid drugs, or liquid medical or biological samples. A vial may be transparent enough to allow the liquids contained therein to be viewed from the outside. A vial may be made of a brittle material, such as glass. Vials made of plastic materials are also known.
A spirit level vial is known in the art that is almost completely filled with a liquid and includes a small bubble of gas, air for example. The spirit level vial can be mounted to a spirit level base. One of the vial or base can include a mark positioned so that when the base is “level”, the bubble will be aligned with the mark. Such vials are not generally subject to high internal pressures.
WO 2004/044524 offered an alternative to this traditional spirit level vial. In this document, a spirit-level is provided that comprises a transparent spirit-level vial, essentially completely filled by a first liquid medium and further contains a globule of a second liquid. The globule can move through the medium in response to changes in the spatial orientation of the vial. The two liquids are airlessly sealed in the vial.
WO 2004/044524 teaches that by careful selection of the type and colour of the second liquid used to form the globule, it is possible to obtain improved visual contrast as compared to with an air bubble, which was traditionally used instead of the globule. In particular, the first and second liquids should have distinctly different densities, e.g. different by at least 0.3 g/cc.
The spirit level of WO 2004/044524 includes a base element to which one of the spirit level vials is mounted. One or more markings are provided on the vial or the base element. The markings are calibrated so as to indicate that a surface upon which the base element rests is level (e.g. horizontal or vertical) when the liquid globule is aligned with the one or more markings.
As the liquids are hermetically sealed in the vial, pressure inside the vial will vary due to temperature changes (i.e. due to thermal expansion). The pressure increase in the vial due to thermal expansion can be calculated as follows, using a nominal example of water as the liquid contained in the vial. The compressibility of water at 20° C. is about 4.5*10−5 bar−1. The thermal expansivity of water is about 0.2*10−3K−1. The ratio of these values leads to the proportion between pressure and temperature change, which is 4.44 bar/K. Thus, if the vial is subjected to a temperature change from 15° C. to 55° C. the pressure inside the sealed vial can reach 180 bar, which would cause many prior art vials to break.
It can thus be seen that the increase in pressure in the airlessly sealed spirit level vial of WO 2004/044524 due to an increase in temperature could be problematic. This problem is applicable to airlessly sealed vials in general and is not just limited to airlessly sealed spirit level vials. Pressure changes in the liquid will put strain on the vial, which can lead to breakage of the vial or put certain constraints on the strength of the material used to make the vial.
There is therefore a need to provide an airlessly sealed vial which can overcome the above problems and this is an object of the present invention.
Further objects and advantages of the vial described herein will become apparent from the following description.